Twelver Shia Islam, known as Ithnā'ashariyyah, is the largest branch of Shia Islam, distinguished by the belief in a succession of twelve Imams as spiritual and political successors to the Prophet Muhammad. These Imams are considered infallible leaders with divine insight, and the line ends with the Twelfth Imam, Muhammad al-Mahdi, who is believed to be in occultation and will reappear as the Mahdi to bring justice to the world.